Logging-While-Drilling (LWD) is widely used in oil and gas drilling and formation evaluation. LWD collects information such as formation resistivity, gamma ray, neutron porosity, borehole caliper, well inclination during the drilling process and transmits the real-time information to the surface, which can be used to guide geosteering.
LWD has been continuously improving in the past decades so that its accuracy and reliability are comparable to those of wireline logging. For example, in the earlier days, electromagnetic resistivity measurement tools operated at 2 MHz. The formation resistivity was combined with natural gamma ray readings to detect distinct changes in the formation and to locate the pay zone so that the drilling tool could be steered to maximize its trajectory inside the pay zone. However, the formation being measured can often be more than ten meters above the drill bit using conventional logging tools, which renders it inadequate for real-time geosteering.
More recently, deep-reading electromagnetic measurement tools become available, which can detect formation information more than 5 meters into the formation. This enables the determination of formation boundary further down so that the drilling tool could be guided to avoid the oil/water reservoir boundary or cap rocks.
Consequently, there is a need for drilling systems and methods that utilize a combination of measurement tools in order to more accurately measure the formation information and guide geosteering.